I'll not say I can answer your two questions but I've been through the
process of formulating a theory and disproving my own theory and formulating
a new theory which is the same process Darwin went through except he didn't
have enough evidence to go on to make adjustments. Darwin simply connected
the dots and today we have more dots to be connected. If he had the dots of
observation he have accumulated to date my guess is that he too would have
gone in a different direction - more toward punctuated equilibrium for
example.

Lynn Margulis has come up with something new called "symbiogenesis."
Simply put, at the microscopic level a wavy swimming organism encounters a
blobby organism and invades it to become a wavy-blobby organism forming a
new species combined from two existing species. This has been detected
apparently and could explain some things pure Darwinian evolution could not.
If this theory gains traction in the scientific community it could dig a
deeper hole for Darwin's gradualism, or perhaps not as what happens at the
microscopic level stays at the microscopic level.

The driving force of evolution today is seen as selection which is not
random versus genetic drift which is seen as entirely random. I agree there
appears to be instances where organisms adapt quickly and it would be
tempting to attribute the changes to adaptive alterations in the genes or
the DNA, but that's an idea out of favor at the moment.

Let me quote from Eugene Koonin's recent paper, "Darwinian evolution in the
light of genomics" (Nucleic Acids Research, 2009, 1-24). These are twp
excerpts from where he is outline the principal concepts of the Modern
Synthesis.

"Evolution proceeds by fixation of the rare beneficial variations and
elimination of deleterious variations: this is the process of natural
selection that, along with random variation, is the principal driving force
of evolution according to Darwin and the Modern Synthesis. Natural selection
which is, obviously, akin to and inspired by the 'invisible hand' (of the
market) that ruled economy according to Adam Smith, was the first mechanism
of evolution ever proposed that was simple, plausible, and did not require
any mysterious innate trends. As such, this was Darwin's second key insight.
The founders of population genetics, in particular, Sewall Wright,
emphasized that chance could play a substantial role in the fixation of
changes during evolution not only in their emergence, via the phenomenon of
genetic drift that entails random fixation of neutral or even deleterious
changes. Population-genetic theory indicates that drift is particularly
important in small populations that go through bottlenecks (6,16). However,
the Modern Synthesis, in its 'hardened' form (13), effectively, rejected
drift as an important evolutionary force, and adhered to a purely
adaptationist model of evolution (17)."

And

"The beneficial changes that are fixed by natural selection are
'infinitesimally' small, so that evolution proceeds via the gradual
accumulation of these tiny modifications. Darwin insisted on strict
gradualism as an essential staple of his theory: 'Natural selection can act
only by the preservation and accumulation of infinitesimally small inherited
modifications, each profitable to the preserved being . . . If it could be
demonstrated that any complex organ existed, which could not possibly have
been formed by numerous, successive, slight modifications, my theory would
absolutely break down.' [(1), chapter 6]. Even some contemporaries of Darwin
believed that was an unnecessary stricture on the theory. In particular, the
early objections of Thomas Huxley are well known: even before the
publication of the Origin Huxley wrote to Darwin ''You have loaded yourself
with an unnecessary difficulty in adopting Natura non facit saltum so
unreservedly' (18)."

Here are my two questions:

Why did Darwin insist on strict gradualism as an essential staple of his
theory?

Why did most proponents of the Modern synthesis reject drift as an important
evolutionary force, and adhered to a purely adaptationist model of
evolution?

- Mike

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Received on Wed Apr 15 14:46:36 2009